Plant Science & Landscape Architecture Theses and Dissertations
Permanent URI for this collectionhttp://hdl.handle.net/1903/2797
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Item Nitrogen cycling by grass-brassica mixtures in the Mid-Atlantic(2019) Gaimaro, Joshua Ruben; Tully, Kate; Plant Science and Landscape Architecture (PSLA); Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)Mixtures of cover crop species may be more effective than monocultures at internal nutrient cycling due to their ability to occupy different niches. Our study investigates nitrogen (N) cycling of radish (Raphanus sativus L.) and rye (Secale cereal L.) in monocultures and mixtures compared to a no cover crop control. The study was established on fine-textured soils near Laurel, MD where we estimated N leaching losses, quantified mineral soil N (to 60 cm), and cover crop biomass N for two years. Forage radish suppressed estimated N leaching in the fall, while cereal rye suppressed estimated N leaching in the spring. In this study, growing radish in a mixture with rye decreased the risk of N leaching losses and enhanced N cycling due to the difference in timing of N uptake and release. Our research indicates that grass-brassica mixtures are a flexible management tool for mitigating N leaching in the Mid-Atlantic.Item Bt GENETICS EFFECT ON CORN HYBRID PERFORMANCE: A COMPARISON OF TWO NEAR ISOLINE CORN HYBRIDS(2018) Thorne, Louis; Kratochvil, Robert J; Plant Science and Landscape Architecture (PSLA); Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)Most corn (Zea mays L.) hybrids planted in the U.S. are the result of genetic modification that gives them a Bt gene or genes obtained from the bacterium, Bacillus thuringiensis (Berliner) (Bt), that express insecticidal proteins and enables these hybrids to be resistant to several insects. European corn borer (ECB) (Ostrinia nubilalis, Hübner) is the main Lepidopteran pest targeted by the Bt corn technology. All Bt events used in current corn hybrids provide 100% control of ECB. This has led to widespread use of Bt hybrids and has resulted in a drastic decrease in the ECB population. This raises the question whether it is still economically feasible to plant Bt hybrids that have higher seed costs in environments where the ECB pest level is low. The objectives of this study were: 1) compare the yield and agronomic performance of a pair of corn near-isoline hybrids with and without the ¬Bt traits; and 2) evaluate the agronomic and economic optimums for yield and nitrogen (N) rate for each near-isoline hybrids. A two-year study at three University of Maryland research farms in 2013-2014 examined each hybrid type for stalk damage due to ECB, yield performance, the optimum N rate for maximizing yield, and the economic returns the two hybrids provided. This study found minimal ECB stalk damage and no consistent agronomic or economic yield difference between the Bt and non-Bt hybrids. Neither hybrid type was determined to have a consistent nitrogen use efficiency (NUE) advantage. The results of this study indicate that producers should not have concerns over hybrid type choice, now that there is significant regional suppression of ECB below economic levels.Item MANAGING WATER, NITROGEN, AND ALLELOPATHY WITH A CEREAL RYE COVER CROP(2018) Otte, Briana; Tully, Katherine L; Plant Science and Landscape Architecture (PSLA); Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)A cereal rye (Secale cereale) cover crop is a multi-functional tool in a no-till corn agroecosystem. The objectives of this study were to (1) quantify soil phenolic acid concentration under cereal rye shoots and roots, and how tillage impacts their release (2) evaluate the effects of cereal rye termination date on soil water, nitrogen, and corn performance compared to no cover crop. Soil phenolic acids have known allelopathic effects, inhibiting some weed seed germination or growth. Results suggest that cereal rye roots release more phenolic acids into the soil than cereal rye shoots, a novel finding. Results also suggest that corn grain yield following a late-terminated cereal rye cover crop is mediated by precipitation pattern and N release from cereal rye residues. During years of above average summer precipitation a late-terminated cereal rye cover crop does not affect corn grain yields and decreases residual inorganic soil N in the agroecosystem.Item Bacterial communities of the specialty crop phyllosphere: response to biological soil amendment use, rainfall, and insect visitation(2016) Allard, Sarah Michelle; Micallef, Shirley A; Plant Science and Landscape Architecture (PSLA); Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)Microorganisms in the plant rhizosphere, the zone under the influence of roots, and phyllosphere, the aboveground plant habitat, exert a strong influence on plant growth, health, and protection. Tomatoes and cucumbers are important players in produce safety, and the microbial life on their surfaces may contribute to their fitness as hosts for foodborne pathogens such as Salmonella enterica and Listeria monocytogenes. External factors such as agricultural inputs and environmental conditions likely also play a major role. However, the relative contributions of the various factors at play concerning the plant surface microbiome remain obscure, although this knowledge could be applied to crop protection from plant and human pathogens. Recent advances in genomic technology have made investigations into the diversity and structure of microbial communities possible in many systems and at multiple scales. Using Illumina sequencing to profile particular regions of the 16S rRNA gene, this study investigates the influences of climate and crop management practices on the field-grown tomato and cucumber microbiome. The first research chapter (Chapter 3) involved application of 4 different soil amendments to a tomato field and profiling of harvest-time phyllosphere and rhizosphere microbial communities. Factors such as water activity, soil texture, and field location influenced microbial community structure more than soil amendment use, indicating that field conditions may exert more influence on the tomato microbiome than certain agricultural inputs. In Chapter 4, the impact of rain on tomato and cucumber-associated microbial community structures was evaluated. Shifts in bacterial community composition and structure were recorded immediately following rain events, an effect which was partially reversed after 4 days and was strongest on cucumber fruit surfaces. Chapter 5 focused on the contribution of insect visitors to the tomato microbiota, finding that insects introduced diverse bacterial taxa to the blossom and green tomato fruit microbiome. This study advances our understanding of the factors that influence the microbiomes of tomato and cucumber. Farms are complex environments, and untangling the interactions between farming practices, the environment, and microbial diversity will help us develop a comprehensive understanding of how microbial life, including foodborne pathogens, may be influenced by agricultural conditions.Item MOWING TO GROWING: TRANSFORMING A MUNICIPAL GOLF COURSE TO URBAN AGRICULTURE IN BALTIMORE CITY(2016) Allen, Nathan; Kweon, Dr. Byoung-Suk; Plant Science and Landscape Architecture (PSLA); Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)This thesis demonstrates how landscape architects can transform underused golf course facilities located within cities for urban agriculture (UA). In the last decade more than 1000 golf courses have closed in the United States. Municipal golf courses represent some of the largest pieces of open space in cities and because of their inherent infrastructure they can provide the ideal location to support large-scale UA. In Southwest Baltimore large food deserts are a serious health concern and represent a lack of access to healthy food options for residents. Carroll Urban Agriculture Park is a design response resulting from a detailed analysis of the existing Carroll Park Golf Course and the surrounding community of Southwest Baltimore. The design will create an urban farm in a park-like setting to provide readily accessible healthy food options and various educational opportunities, and to support current and future urban agriculture related businesses in Baltimore.Item EFFECT OF COMPOST ON THE MICROCLOVER ESTABLISHMENT AND USE OF COMPOST AND MICROCLOVER TO REDUCE LAWN NUTRIENT RUNOFF(2016) Xiao, Xiayun; Carroll, Mark; Plant Science and Landscape Architecture (PSLA); Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)High volume compost incorporation can reduce runoff from compacted soils but its use also associated with elevated N and P concentrations in runoff making it difficult to assess if this practice will reduce nutrient loading of surface waters. Additionally, little is known about how this practice will effect leguminous species establishment in lawns as means to reduce long term fertilizer use. When 5 cm of compost was incorporated into soil a reduction in runoff of 40 and 59% was needed for N and P losses from a tall fescue + microclover lawn to be equivalent to a non-compost amended soil supporting a well fertilized tall fescue lawn. Use of compost as a soil amendment resulted in quicker lawn establishment and darker color, when compared to non-amended soil receiving a mineral fertilizer. Biosolid composts containing high amounts ammonium severely reduce the establishment of clover in tall fescue + micrclover seed mixture.Item Genetic Control of Flowering Time in a Soft Red Winter Wheat Doubled Haploid Population(2015) Miller, Daniela Michelle; Costa, Jose M; Plant Science and Landscape Architecture (PSLA); Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)Flowering time in wheat is regulated mainly by response to seasonal environmental cues and controlled by the photoperiod and vernalization pathways. Allelic diversity in genes controlling these pathways is used by breeders to adapt wheat for optimal yield in a broad range of environments. This study characterized genetic loci influencing heading date in a soft red winter wheat doubled haploid population. Two photoperiod insensitivity alleles, Ppd-A1a and Ppd-D1a, were found to have major effects in eight field locations. The Ppd-A1 locus explained up to 16.8% of variation in heading date, whereas the Ppd-D1 locus explained up to 39.7%. In reduced vernalization greenhouse experiments, a QTL in the same region as the VRN-A1 gene explained up to 42.4% of variation in heading date, suggesting that the population differed in this region. Assays for previously-described allelic diversity in the VRN-A1 gene, however, did not detect any polymorphism between parents of the population.Item EVALUATION OF COMPOST TOPDRESSING, COMPOST TEA AND CULTIVATION ON TALL FESCUE QUALITY, SOIL PHYSICAL PROPERTIES AND SOIL MICROBIAL ACTIVITY(2015) Chen, Siqi; Carroll, Mark J.; Plant Science and Landscape Architecture (PSLA); Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)Compost topdressing, compost tea, and hollow tine cultivation are common cultural practices employed in organic lawn care programs. Restrictions on the amount of bagged fertilizer nitrogen and phosphorus applied to turf have raised questions about the need to place similar restrictions on compost turfgrass applications. In a three-year study the effect of reduced and common practitioner use rates of compost topdressing, the use of compost tea and of hollow tine cultivation on soil physical and biological properties and turfgrass quality were evaluated. Cultivation, monthly compost tea application and compost topdressing applied at rates consistent with annual bagged fertilizer nitrogen restrictions had little effect on soil organic matter, microbial activity, bulk density and infiltration. The use of a synthetic fertilizer resulted in higher turf quality than the use of compost on most evaluation dates. Nutrient fertilizer restrictions if applied to compost will likely result in a decline in turf quality.Item Effects of a Simulated Dicamba Misapplication on Non-tolerant Soybeans (Glycine max)(2015) Morris, Matthew; Ritter, Ronald L; Plant Science and Landscape Architecture (PSLA); Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)Approval is pending for the registration of dicamba tolerant (DT) soybeans [Glycine max (L.) Merr.]. The use of dicamba on DT soybeans and other DT crops will increase. Risks associated with dicamba applications include off-target movement to sensitive crops. The objective of this study was to evaluate misapplication of dicamba on non-DT soybeans. Greenhouse and field studies examined a rate titration (0.004 to 0.5 lb ai a-1) of dicamba on non-DT soybeans (V3 stage - three trifoliates). Field studies also examined dicamba application to various growth stages (PRE- preemergence to R5- early pod fill) of non-DT soybeans. Results from the greenhouse and field studies showed that as the rate of dicamba increased, the level of injury to vegetative and yield components also increased. Soybean growth stage at time of application influenced the amount of injury. Less injury was observed when dicamba was applied at the PRE growth stage.Item Nitrogen Management in Corn: Influences of Urea Ammonium Nitrate (UAN) Applications With and Without Nitrogen Stabilizer Products.(2013) Watkins, Patrick Howard; Kratochvil, Robert J; Plant Science and Landscape Architecture (PSLA); Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)Corn (Zea mays, L.) is a major crop produced in the nutrient sensitive Mid-Atlantic region. Nitrogen use efficiency (NUE) for corn is considered sub-optimal and farmers in the region use a number of best management practices (BMPs) to improve corn NUE. Two sidedress application methods (surface banding and sub-surface injection) and four commercially available nitrogen stabilizer products (`Agrotain', `Agrotain Plus', `Instinct', `Nutrisphere-N') were investigated during 2009-2011 over three N fertilizer rates at nine total locations. Headspace ammonia accumulation (post-sidedress) was indexed to the surface applied UAN treatment and resulted in application method and stabilizer products having a significant effect for headspace ammonia accumulations. Post-harvest inorganic soil nitrogen was not affected by application method or stabilizer products. Yield was not significantly affected by application method or stabilizer products but was affected by N rate. Total plant N concentration was not significantly affected by application method or stabilizer products.